In recent years, there have been increased interests on information security, and information processing devices including a fingerprint sensor for fingerprint authentication have been widely used (for example, see Japanese Laid-open Patent Publication No. 2001-265507). An information processing device including a fingerprint sensor is configured so that important processes such as login are not performed if fingerprint authentication fails. Thus, it is possible to effectively prevent information leakage, etc., to a third person.
Some of fingerprint sensors included in portable terminals such as a mobile telephone are used not only for fingerprint authentication but also for operation inputs. A fingerprint sensor is provided with a function of inputting operations as in a touch panel so as to allow for operations such as a drag and a double tap. Thus, as compared to operations achieved solely by button operations, a user of the portable terminal can easily use a high-function application such as a WEB browser.
When utilizing a fingerprint sensor for operation inputs, besides for fingerprint authentication, there has been a case in which the fingerprint sensor detects an operation not intended by a user, resulting in an erroneous operation in an information processing device such as a portable terminal. In a case where the fingerprint sensor can detect whether or not a finger of a user is placed on the fingerprint sensor and can detect a distance along which the finger moves on the fingerprint sensor and the direction thereof, but cannot determine whether the user has intentionally touched the fingerprint sensor, if the finger of the user touches the fingerprint sensor while holding the information processing device with a hand without paying attention to the fingerprint sensor, for example, such an unintentional operation is detected by the fingerprint sensor and recognized by the information processing device, thereby causing an erroneous operation.